European debut of intrinsic safety breakthrough

For 40 years intrinsic safety (EX i) has meant limiting the amount of electric power to less than 2 Watts in dangerous areas, for fear any spark could ignite an explosion. As a result, an entire industry of companies has developed that supply isolators and barriers to provide this type of protection.

Michael Babb, Control Engineering Europe

07/01/2008

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For 40 years intrinsic safety (EX i) has meant limiting the amount of electric power to less than 2 Watts in dangerous areas, for fear any spark could ignite an explosion. As a result, an entire industry of companies has developed that supply isolators and barriers to provide this type of protection. At Interkama, one of the co-located shows that was part of Hannover Industrial Fair this year, two of these companies were showing a new approach that could potentially alter the future of EX i practice.

MTL Instruments Group, based in Luton, England, U.K., and Pepperl + Fuchs, with world headquarters in Mannheim, Germany, were displaying technology that allows comparatively large amounts of power—50 Watts and beyond—into areas that were previously considered too dangerous for live electricity.

The new method uses fast electronics to monitor fieldbus circuits and detect surges in current and voltage that are characteristic of a suddenly broken line or a module being unplugged from a backplane.

Sparks always lead to a sudden peak of the current and voltage within the respective circuit, and these peaks show very specific characteristics. Electronics can detect those characteristics within five microseconds and shut down the power supply. The idea is to shut off power before a critical situation can arise, and before the current can reach a level to build up sufficient heat for ignition.

For its efforts, Pepperl+Fuchs was one of five Hermes Award finalists at Hannover Messe (winners of the Hermes Award, the world's largest technology prize, receive 100,000 Euros). Its system is called DART, for dynamic arc recognition and termination.

Dipl-Ing Thomas Kleinbongartz, Pepperl+Fuchs director of global marketing, says his company will offer DART in two versions: one is for high-power devices up to 50 Watts inside the Ex i area, such as industrial PCs, LED lighting systems, analysis instruments, and solenoid valves. A second system will offer, via a fieldbus infrastructure, up to 8 Watts of electric power per segment inside explosion hazardous areas.

Factors such as cable length and device characteristics can greatly influence the response time for spark detection, says Kleinbongartz. DART deals with these differences by connecting the device via a decoupling module to the energy supply. The module ensures a clearly defined electrical response pattern, always providing the DART system with a signal that allows the dependable detection of critical situations requiring immediate shutdown of the circuit, he said.

MTL Instruments Group managing director Graeme Philp was on hand to introduce his company's version of the concept called “Fast Switch.” MTL will implement the technology in conjunction with the MTL PoEx Intrinsic Safety Ethernet range, which was a major product launch at Interkama.

“The ability to run fieldbus networks over a longer distance while maintaining the ability to live work is solved by the use of certified switching components that permit the safe interruption of non-intrinsically safe circuits,” Philp said. “This, together with the launch at Interkama of redundant power for FISCO (Fieldbus Intrinsically Safe Concept) networks, allows users to enjoy the highest availability on the market, while retaining the ability to live work in applications requiring long cable lengths.”

At a Fieldbus Foundation seminar in Houston, TX, also in April 2008, Philp showed MTL's F809F Fieldbus diagnostics module. At that time, MTL Instruments was three months into its acquisition by U.S.-based Cooper Industries and Philp told Control Engineering , “It's really going well. This purchase has not limited our independence.” Philp characterizes the transition as highly complementary and beneficial for customers. “There's not a single product overlap,” he said.

Author Information

Michael Babb is editor of Control Engineering Europe. Reach him through